When an image of a bright object is captured by an imaging device that captures an object, unnecessary light in a captured image can be large enough to be visible, adversely affecting the captured image. Especially when a diffractive lens having a diffraction grating is used, the unnecessary light can be larger than when an aspheric lens is used. For example, unnecessary light that looks like a double image can appear in the captured image, when a light source such as a fluorescent lamp is captured.
Examples of conventional techniques that reduce such unnecessary light by image processing include techniques described in Patent Literatures (PTLs) 1 and 2. According to PTL 1, the unnecessary light is estimated based on a convolution integral of a captured image and a point spread function (PSF) image of unnecessary order light (zeroth order light and second order light) of a diffractive lens. Then, the estimated unnecessary light component is subtracted from the captured image. The unnecessary light is thus reduced from the captured image.
According to PTL 2, a plurality of images is captured with different exposure times. The unnecessary light is estimated based on an image captured with a short exposure time, and the estimated unnecessary light component is subtracted from an image captured with a long exposure time. The unnecessary light is thus reduced from the image captured with a long exposure time.